This invention relates to turbochargers for supplying relatively high pressure charge air to an internal combustion engine. More specifically, this invention relates to a turbocharger control including means for controllably preventing the delivery to an engine of charge air above a predetermined pressure level, and for maintaining the charge air substantially at that predetermined level.
Turbochargers are well known in the prior art, and typically comprise a turbine wheel and a compressor wheel mounted on a common shaft and carried within isolated turbine and compressor housings. The turbine housing includes a gas inlet and a gas outlet, and is coupled to the engine exhaust gas manifold for circulation of the exhaust gases through the turbine housing to rotatably drive the turbine wheel. In turn, the turbine wheel rotatably drives the compressor wheel which compresses wheel ambient air and supplies the compressed air to the intake manifold of the engine. Importantly, the gas outlet of the turbocharger housing is typically coupled to an exhaust gas discharge housing which is in turn coupled to exhaust system conduits which may include pollution and noise control equipment.
The use of turbochargers is highly advantageous when compared with conventional naturally aspirated engines in that substantially higher density fuel-air mixtures may be delivered to the engine cylinders. This increased fuel-air density results in substantially improved engine performance and efficiency. However, with many internal combustion engines, it is desirable to limit the maximum pressure at which charge air may be delivered to the engine, and to maintain the delivery of charge air at that maximum pressure level. That is, many turbochargers are capable of delivering charge air to the engine at pressures substantially greater than the engine or the turbocharger can withstand. Accordingly, a wide variety of valves and other pressure control devices have been proposed to limit the maximum discharge pressure, or boost, of the turbocharger compressor.
Turbocharger boost controls typically comprise valved apparatus, commonly referred to as a waste gate valve, for bypassing a portion of the engine exhaust gases around the turbine wheel. In this manner, a portion of the exhaust gases is prevented from driving the turbine wheel so that the turbine wheel rotates at less than maximum speed whereby the compressor wheel is also driven at less than maximum speed. Structurally, some of these bypass devices comprise a bypass passage integrally cast as part of the turbine housing and a bypass or waste gate valve mounted directly on the turbine housing. See, for example, U.S. Pat. Nos. 3,195,805; 3,196,606; 4,005,578; and 4,005,579. These bypass devices are disadvantageous, however, in that they require relatively complicated and expensive turbine housing castings together with relatively expensive metering valves machined to close manufacturing tolerances. Other bypass devices have been proposed which remove the bypass passage and the valve from the turbine housing. See, for example, U.S. Pat. Nos. 3,035,408; 3,096,614, 3,104,520; and 3,389,553. However, these devices all require separate specially constructed and relatively complicated bypass conduit constructions mounted on the turbine housing, and do not eliminate the need for expensive metering valves.
The present invention overcomes the problems and disadvantages of the prior art by providing a turbocharger with boost control wherein the turbine housing casting is simplified, and wherein separate bypass conduit constructions and close valve tolerances are eliminated.